1. Field of the Invention
The present invention pertains to a nut for coupling a flared tube to a flared fitting, and more particularly, pertains to a nut which is capable of withstanding a wide range of temperature excursions without disintegrating or thermal creeping.
2. Description of the Prior Art
The prior art devices offer a coupling scheme consisting of a vessel or container of PFA or PVDF fitting which is capable of withstanding temperatures up to 180.degree. C., and flared tubing of TEFLON or PFA which is similarly rated. The nuts, however, of PFA or PVDF do not offer temperature range compatibility when exposed to strong oxidizers, such as sulfuric acid, of the nuts of PVDF. The nuts of PVDF cannot withstand high temperature or wide temperature excursions and tend to disintegrate. The nuts of PFA, while capable of high temperature excursions, and resisted disintegration, but would tend to unscrew or creep, thus violating the integrity of the seal.
The prior art attempts to solve the creep issue include high temperature plastics such as PEEK (Poly Ethyl Ethyl Ketone) and others. These were not compatible with the strong oxidizers, such as sulfuric acid or with hot solvents. Attempts were made by Nisso of Japan to TEFLON coat these polymers, but it did not work too well due to pinholes, etc. Asti Corporation of France also produced flare fittings for the European market, but also did not solve the high temperature opportunity. Later, Fluoroware Corporation adopted the flare methodology and included some of the PVDF and TEFLON, etc. fluoropolymer materials loaded with various fibers to add rigidity, where some of these ideas included carbon and glass, but these also did not work well. The creep issue still prevailed until this invention.
The present invention overcomes the failings of the prior art by providing a ceramic nut which withstands a large range of temperature excursions without failure or creeping.